<?php
/**
 * 生成验证码
 * @param int $type
 * @param int $length
 * @return string
 */
function  buildRandomString($type = 1,$length = 4){
    if ($type == 1) {
        $chars = join("", range(0, 9));
    } elseif ($type == 2) {
        $chars = join("", array_merge(range("a", "z"), range("A", "Z")));
    } elseif ($type == 3) {
        $chars = join("", array_merge(range("a", "z"), range("A", "Z"), range(0, 9)));
    }
    if ($length > strlen($chars)) {
        exit("字符串长度不够");
    }
    $chars = str_shuffle($chars);
    return substr($chars, 0, $length);
}

/**
 * 生成唯一字符串
 * @return string
 */
function getUniName(){
    return md5(uniqid(microtime(true),true));
}

/**
 * 得到文件扩展名
 * @param string $filename
 */
function getExt($filename){
    $temp=explode(".", $filename);
    return strtolower(end($temp));
}



